Srimad Bhagvata Mahapurana: Book 10: Chapter 36: Verses 1-12
Kamsa sends Akrura to Vraja to bring Sri Krsna and Balarama to Mathura
Sri Suka began again : Some time after (Sri Krsna's return from the forest) there came to Vraja Arista, a demon disguised as a bull with a huge body and a large hump, shaking the earth (already) torn by his hoofs. He was bellowing very harshly and breaking the earth with his hoofs; (nay,) uplifting his tail he was throwing up the mounds of earth with the ends of his horns and was (at the same time) discharging dung and urine in small quantities (at intervals), and staring with unwinking eyes. At his violent and thunder-like roar, 0 dear Pariksit, cows and women were prematurely delivered of their offspring at an initial or advanced stage of gestation indeed through fear, and clouds settled on his hump mistaking it for a hillock. Perceiving that animal with sharp horns the cowherds and cowherdesses felt dismayed and the cattle fled in terror leaving Vraja far behind, 0 king Crying "Krsna! O Enchanter of all !!" they all sought Govinda as their refuge. Observing this and reassuring the people of Vraja, driven off by fright, in the words "Do not be afraid !" the Lord too challenged the diabolical bull saying, "What will you gain, 0 fool, through the cattle and the cowherds being terrified thus, O vilest creature ?